(d)(i) Describe a chemical test that could be used to distinguish between pure water and sodium tetraoxosulphate(VI)solution
(ii) Zn(OH)2 and Ca(OH)2 are white substances What reagent would be suitable to distinguish between the two substances? [ 4 mark s ]

The question was attempted by most candidates and the performance was poor.

In part (a), candidates were unable to outline how a mixture of ammonium chloride,
potassium chloride and lead (II) chloride could be separated in the laboratory. The
expected answers from candidates were as follows:

- Pour the mixture into an evaporating dish and cover with a glass funnel.
- Heat the mixture
- Ammonium chloride sublimes and collects in the funnel
- Add distilled water to the mixture
- Potassium chloride dissolves
- Filter and collect the lead (II) chloride as residue
- Evaporate the filtrate to dryness to obtain potassium chloride.